BIOLOGY UNIT 4: EDEXCEL IAL PPQs

Describe the structures in a chloroplast that are involved in the light-dependant reactions of photosynthesis.

1) ref. to thylakoids.
2) made of membranes.
3) arranged as stacks/grana/eq.
4) contain chlorophyll}/eq.
5) arranged as photosystems.

Suggest 2 advantages of growing crops of wheat in glasshouses with artificial lighting rather than growing them in open fields.

1) crops can be grown out of season/all year round/eq.
2) plants can photosynthesise 24 hours a day/eq.
3) idea of less physical damage from weather/animals/eq.
4) pest control easier/eq.
5) ref. to control of other named factor (e.g CO2, temperature, humidity, water supply).

Explain how the increases in CO2 and CH4 released into the atmosphere may be contributing towards the estimated changes mean temperature.

1) CO2 and CH4 are both greenhouse gases.
2) trap/absorb heat/IR/long-wave radiation /eq.
3) idea of reflected form Earths surface/ re-radiation.
4) mean temperature of Earths surface increases/eq.

Suggest why higher and lower estimates of global temperatures are made.

appropriate comment on changes in production of gases e.g higher estimate assumes no change in production of gases/ lower estimate takes into account reduction in carbon emissions.

Name and describe the structures where the polypeptide chain of an enzyme would be synthesised.

1) ribosomes/RER
2) descriptive feature e.g (for ribosome) - 2 subunits (for RER) ribosome attached to membrane.

Explain what is meant by gene mutation

1) change in DNA
2) ref. to change/deletion/addition/duplication/substitution/eq. of bases/nucleotides.

Theory used in DNA profiling

1) DNA profiling assumes everyones DNA is unique/different/eq.
2) apart from identical twins/eq.
3) ref. to DNA profiling analyses the introns/nc-blocks/short tandem repeats/eq.
4) nc-DNA is very variable/eq.
5) large number of introns/nc-blocks/eq.
6) idea of many combinations/eq. at each locus.

Explain why evidence from DNA profiles may not be absolutely conclusive.

1) ref. to DNA profiling has several stages.
2) ref. to contamination/eq. can arise at any stage.
3) only a few sequences/small portion of DNA is analyses/eq.
4) ref. to possibility of 2 identical profiles form unrelated individuals.
5) identical twins/closely related individuals/eq. may show same profile/eq.

Suggest hoe DNA profiling could be useful to scientists who examine fossils of animals and plants

1) comparisons made between DNA from fossils and other organisms.
2) to find genetic relationships/eq.
3) ref. to use in taxonomy/ classification/eq.
4) to understand evolutionary lines/ to determine common ancestors/eq.

State how the genetic material in HIV differs from the genetic material in the
bacterium Mycobacterium tuberculosis that causes TB.

1) RNA in HIV and DNA in M.TB/eq.
2) comparative description of nucleic acid (e.g circular in M.TB and linear in HIV).
3) plasmids in M.TB and no plasmids in HIV.

Explain why unbroken skin is an effective barrier against HIV infection

1) keratin in skin surface/epidermis.
2) idea of forms a hard/ impenetrable/ physical/ eq. barrier.

Explain the decrease in numbers of CD4 T-lymphocytes during the first 6 weeks after infection with HIV.

1) glycoprotein on virus/ eq.
2) binds with receptors/CD4/eq.
3) on membrane of lymphocytes/ eq.
4) viral RNA enters the lymphocyte/ eq.
5) viral RNA used to produce viral DNA (in lymphocyte/eq.
6) by action of reverse transcriptase.
7) ref. to formation of new viruses.
8) lymphocytes destroyed when new viruses bud out of/ leave the cell/eq.
9) T-killer cells destroy T-helper cells.

Explain how CO2 + ammonia are formed during the first stage of decomposition (putrefaction).

1) ref. to MO/ microbes/ bacteria/ fungi/eq.
2) ref. to respiration of MO/ bacteria/ fungi/eq.
3) ref. to aerobic/ anaerobic respiration.
4) converts organic compounds/eq. to CO2.
5) converts nitrogen compounds/ proteins/ amino acids/ urea to ammonia/eq.

Suggest why time taken for decomposition changes at different times of the year.

1) correct ref. to temperature effect.
2) correct ref. to water availability.
3) correct ref. to water logging reduces O2 availability/eq.
4) correct ref. to frozen water.
5) ref. to more insects/ decomposers/ eq. in summer.
6) correct ref. to the growth rate of MOs/ eq.
7) ref. to rate of metabolism/ enzyme reactions.

Explain what is meant by the terms bacteriostatic and bactericidal antibiotics

1) idea of antibiotic is used to control/ kill/ prevent reproduction/ eq. of bacteria.
2) bacteriostatic prevent reproduction/ division/ multiplication/ growth/ eq. of bacteria.
3) bactericidal destroy/ kill bacteria.

How to control spread and decrease hospital acquired diseases

1) hand washing regimes for medical staff/ visitors.
2) particularly when dealing with open wounds/eq.
3) ref. to wearing suitable clothing.
4) ref. to antiseptic readily available.
5) named antiseptic.
6) ref. to isolation of suspected cases/ screening of admissions/ eq.
7) control/ monitoring use of antibiotics.
8) fewer patients/ visitors passing in and out.

Data reliability - reliability decreases when...

1) SD increases.
2) there is variability in SD and so variability in reliability .

Suggest 2 reasons why 95% of the light energy hitting the surface of the leaf is not used by the chloroplasts.

1) idea of reflection.
2) re. to incorrect wavelength/ colour/ freq.
3) idea that light is transmitted/ doesn't hit the chloroplast/ chlorophyll.
4) idea of light being in excess e.g at max. photosynthesis so no more light can be used (other limiting factors).

Explain what is meant by J/m2/year

joules/ energy per square metre/ unit area per year/ unit time.

With reference to the structures in a chloroplast, explain how the energy from light is made available in ATP molecules for the synthesis of organic materials.

1) ref. to thylakoid (membranes).
2) in geranium/ grana.
3) light energy raises energy level of e-/ e- excited.
4) e- released from chlorophyll/ photosystem/ eq.
5) ref. to e- carrier/ eq.
6) ref. to a series of redox reactions/ eq.
7) ref. to e- energy level falls/ eq.
8) ref. to synthesis of ATP from ADP + P (phosphorylation)
9) ref. to photophosphorylation.
10) ref. to ATP synthase/ ase
11) ref. to chemiosmosis/ eq.
12) idea of e- from photolysis used to replace those lost.

Suggest explanations for the effect of temperature on the rate of growth of photosynthetic plants.

1) ref. to enzymes involved in growth.
2) molecules have more KE as temperature increases.
3) there for more enzyme-substrate collision/ rate of collisions increase as temperature increases.
4) correct ref. to denaturation of some enzyme/ protein.
5) rate of growth decreases as fewer enzyme molecules available.

Explain why the process of non specific immune response to bacterial infection will only happen in response to some types of bacteria.

1) ref. to protein nature of antigens/ antibodies.
2) antigens are specific to each bac.
3) antibodies need to be complementary/ specific to the antigen.
4) idea that binding takes place.
5) some bac. have diff. antigens.
6) idea that this is primary infection.
7) ref. to slime capsule of bac. cells.
8) idea that some bac. are inside body cells/ infect body cells.
9) idea that antibodies already present (e.g from passive immunity).

Explain how the formation of mRNA during transcription in the nucleus leads to the synthesis of a sequence of amino acids.

1) DNA strands unzip/ eq.
2) idea that one DNA strand (sense) used as template to form mRNA/ eq.
3) from free nucleotides/ eq.
4) ref. to complementary base pairing.
5) ref. to H-bonding.
6) correct ref. to RNA polymerase/ DNA helicase.

Explain how the translation of mRNA into the sequence of amino acids in a ribosome leads to the synthesis of a sequence of amino acids.

1) ref. to specific amino acid attachment to tRNA.
2) idea that anticodon (on tRNA) attaches/ binds to the codon on mRNA.
3) idea that 2 tRNA held in ribosome at any one time.
4) ref. to formation of peptide bonds between adjacent amino acids.

Suggest why the finial triplet of nucleotides on the mRNA strand doesn't correspond to any anticodon on tRNA.

1) stop codon.
2) used to end the sequencing/ further attachment of tRNA/ eq.
3) release of the polypeptide/ release from the ribosome/ eq.

suggest why some scientists might prefer to classify 2 similar species of plants as varieties within the same species rather than as 2 separate species.

1) idea that individuals of a species can interbreed.
2) to produce fertile offspring.
3) the hybrids/ offspring can flower and produce viable seeds/ eq.

Explain what is meant by the term genetic diversity in a species.

1) variety of alleles.
2) in a gene pool.

Explain why there is likely to be a greater genetic diversity in the hybrid plants than in either of the 2 separate species.

1) different alleles in each of the 2 populations.
2) each population is adapted to live in different environmental conditions/ eq.
3) there will have been different mutations in each population.
4) hybrid offspring will receive alleles from both species.

suggest how woodlice (decomposers of dead plants) are involved in the recycling of carbon.

1) ref. to decomposition of carbon/ organic/ eq.
2) CO2 released (from aerobic respiration).
3) this CO2 is available for photosynthesis.
4) CH4 released (from anaerobic respiration).
5) CH4 available as fuel.

Define hypothesis

An educated guess

Explain why it would be difficult to determine which abiotic factor is affecting the results in a garden habitat.

1) for results to be scientifically valid.
2) only 1 factor needs to be varied/ eq.
3) other factors need to be kept constant/ eq.

4) ref. to many factors (e.g biotic) in a garden.
5) these factors are difficult to control .

name of structure + which type of cell:
enclosed by outer smooth membrane, inner membrane folded making cristae.

mitochondria in eukaryotic cells.

name of structure + which type of cell:
long strand-like structure extending out from the cell; used for locomotion

flagella in both prokaryotic and eukaryotic.

name of structure + which type of cell:
small, circular loop of double-stranded DNA

plasmid in prokaryotic cells.

Suggest how bacterial cells are killed by bactericidal antibiotic.

1) cell wall weaker/ can't form properly.
2) cell wall bursts easily/ eq.
3) during division/ eq.

Explain why doctors have been advised to limit the prescription of antibiotics

1) ref. to AB acting as selective pressure.
2) ref. to some bacteria resistant to AB.
3) idea that resistant bacteria survive and pass of gene for resistance to offspring.
4) idea that AB no longer effective.
5) ref. to some infections can't be treated with AB.

Describe how you could investigate the effect of different ABs on bacteria.

1) idea of bacteria distributed evenly/ description of technique (e.g by lawn spreading).
2) description of method used to apply different ABs at known positions (e.g multi discs, wells in agar)
3) ref. to control of AB conc.
4) ref. to aseptic technique.
5) ref. to incubation at a suitable temperature.
6) description of how effect is assessed (e.g measure clear area/ inhibition zone/ eq.).
7) ref. to repeat with same bacteria.
8) ref. to repeat with diff bacteria.

Site of carbon fixation

stroma of chloroplasts

suggest why the rate of development of a plant depends on the rate of carbon fixation in the plant.

1) idea of carbon fixation produces GP.
2) GP is converted to starch/ sugar/ eq.
3) faster carbon fixation means faster starch/ sugar production/ eq.
4) ref. to rate of development depends on rate of carbon fixation.
5) ref. to increased GPP of crop

what type of cell is a protein coat/ capsid found in?

viruses only.

Describe the chemical nature of cellulose.

1) polysaccharide.
2) unbranched/ straight chain.
3) beta glucose.
4) 1,4 glycosidic bonds.
5) ref. to intermolecular hydrogen bonds.

suggest why some countries may decide to drain their marshy peatlands for the production of biofuels.

1!) ref. to increased income.
2) in order to export fuel.
3) ref. to more jobs.
4) reduce imports of fossil fuels.
5) ref. to biofuels renewable/ sustainable.
6) fossil fuels finite/ eq.
7) as an alternative to fossil fuels/ meeting carbon targets.
8) ref. to no loss of farmland.

Biofuels are considered to be carbon neutral.
Suggest why the continued draining and clearance of peatlands may contribute towards global warming even though they may be used to produce biofuels.

1) ref. to combustion of biofuels releases CO2 removed from atmosphere.
2) therefore there is no net increase in CO2 inn the atmosphere/ eq.
3) CO2 is a greenhouse gas.
4) that absorbs IR radiation (heat).
5) ref. to prevents IR radiation (heat). escaping into space.
6) idea that carbon in peat land was trapped a long time ago.
7) idea of peatland clearance releases CO2.
8) idea that there is a net gain of CO2 in the atmosphere.
9) idea that removal of plants during clearance reduces photosynthesis.
10) ref. to CO2 released from clearance machinery.

state symptoms of TB.

1) coughing.
2) tubercules.
3) bloody sputum.
4) body tissue wastage.

Describe how the organisms that cause TB are taken up by macrophages.

1) idea of bacterium recognised as non-self.
2) ref. to labelling of bacteria by B-cells.
3) phagocytosis.
4) descriptive detail of phagocytosis (involving bacteria)
5) ref. to formation of vacuole.

Ingesting food containing M.TB is unlikely to lead to the development of TB. Give an explanation for this.

1) bacteria killed in stomach.
2) by hydrochloric acid.

Why would quadrats be divided into smaller sections?

1) make it easier to estimate/ measure/ count/ eq.
2) rf. to more precise.

Describe how free nucleotides are bonded together in the correct sequence in pre-mRNA.

1) idea of sequence of bases/ nucleotides on DNA determines sequence on pre-mRNA.
2) ref. to complementary base pairing.
3) ref. to formation of bonds by condensation reaction.
4) phosphodiester bonds.
4) ref. to RNA polymerase

Suggest why a variety of different protein structures could be formed from the polypeptides synthesised using the mRNA molecules from a single gene.

1) ref. to different variations of axons/ mRNA.
2) ref. to different primary structure/ sequence of amino acids.
3) ref. to secondary/ tertiary structure of proteins depends on primary structure/ sequence/ eq.
4) dude to different bonds.
5) hydrogen/ ionic/ disulphide bonds.
6) ref. to different 3D shape/ eq.

Explain what is meant by gene pool

all the alleles in a population.

Explain what is meant by allele frequency

the number of time one allele occurs within a gene pool/ population

Explain how the results of DNA profiling of tissue samples from 2 sub-species can be used to provide evidence that they share a common ancestry.

1) ref. to bands produced.
2) ref. to bands at certain positions.
3) common bands contain similar DNA fragments.
4) idea that the more similar the patterns the closer the relationship.
5) idea that very few differences if still a sub-species

MRSA is a bacterium. when it enter the blood it can stimulate the production of several different clones of plasma cells. These produce a variety of antibodies (polyclonal antibodies).
Suggest an explanation for this.

1) bacterium is made of many different polymers/ chemicals/ eq.
2) which can act as antigens/ eq.
3) ref. to B-cells.
4) ref. to individual B-cells recognise specific antigens/ antibodies are specific/ eq.
5) ref. to activation of B-cells by T-helper cells.
6) ref. to mitosis in B-cells.
7) to form genetically identical plasma cells (clone of plasma cells)

Suggest the advantage of using monoclonal antibodies rather than polyclonal antibodies in the detection of antigens in the blood. Give reasons for you answer.

1) specific antigen/ virus/ pathogen/ bacterium/ eq. can be identified.
2) idea of specific/ monoclonal antibody binds to specific/ only one antigen.
3) specific treatment can be given/ eq.
4) avoids unnecessary use of drugs/ treatment/ eq.
5) more likely to be effective/ eq.